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2-wire to 5-wire furnace hookup

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  • 2-wire to 5-wire furnace hookup

    Sorry if this is an electricians questions rather than an HVAC question: I have a two-wire line running from my 1-stage furnace with no cooling to my thermostat. I am upgrading my thermostat and it needs a C wire. Now, I know there are various ways of hooking up adapters, etc., to compensate for the missing C wire. I could even get another type of thermostat. But because it is a short run from my first floor thermostat to my furnace, I want to replace the old wiring with new wiring. So I am going to get an 18/5 wire. My furnace wiring diagram (Gas-Fired, Direct Vent Condensing) shows R to R, G to G, W to W and B/C to B/C. That's four wires. What do I do with the other one -- the yellow one? Do I hook it up Y to Y even though I don't have a compressor/air conditioning system? Is there anything I'm forgetting? Thanks in advance.

  • #2
    You can just leave it out. Y is usually used to energize the condensing unit in cool but since you don't have ac you cannot use it. It will be available if you decide to get ac in the future.